How Do I Make A Trace Effect Similar to Tron: Legacy Light Cycle Scene
Edit: Cegaton already answered a very similar question here.

You'll find a lot of tutorials on Youtube about light streak effects, there are a lot of ways, it really depends on how it is supposed to look like and how sophisticated you want it to be... I guess in the Tron movie they use several combined effects so even if I knew it would be hard to sum it up in few words. One of the most basic way to make a light streak could be this one:


Create a curve, create a second one that will be its Taper Object (its profile from its start to its end).





In the Properties panel > Data, play with the parameters to give your curve its thickness and its profile. The taper allows you to make the streak slightly disappear at its end.





Play with the End value (and also maybe its Start value) and give it some keyframes to animate.





Now in the Node Editor > Compositing mode, give a blur effect or else to give the glow effect.